Energy may be harvested from the movement of body joints of humans and other animals by converting mechanical energy derived from such movement to electrical energy. Activities where body joints move repeatedly, such as walking, jogging, and running, for example, present opportunities to harvest energy from moving body joints over an extended period of time. In some energy harvesting devices and methods, a generator driven by joint motion is coupled to an electrical load. Since the instantaneous mechanical power provided by body joints during repetitive or cyclical activities varies markedly over the period of each cycle, the harvested electrical power produced also varies markedly over each cycle. For example, the power produced by an energy harvester may on average be 10 W, but it may vary from zero to 60 W multiple times per stride. During a rapid gait, or a change of gait, and where a person is using two energy harvesters, one on each leg, the combined instantaneous output power may reach 120 W.
Intermediate storage capacitors may be used to store the energy produced by energy harvesters, but if these capacitors become fully charged or reach a predetermined voltage limit, then they can no longer accept any more energy. This results in the harvester ceasing to create energy, which in turn causes a sudden drop in the generator torque felt by the user's body joints (e.g. knees), and this causes discomfort to the user.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.